1,007 research outputs found
The discovery and properties of pentaquarks
The pentaquarks are exotic baryons formed of four quarks and an antiquarks.
Their existence has been discussed in the literature over the last 30 years or
more, first in connection with kaon nucleon scattering data. The subject has
been revived by the end of 2002 when experimental evidence of a narrow baryon
of strangeness = + 1, and mass 1530 MeV has been found. This is
interpreted as the lightest member of an SU(3)-flavor antidecuplet. Here we
shall mainly review the predictions of pentaquark properties as e.g. mass, spin
and parity, within constituent quark models.
Both light and heavy pentaquarks will be presented.Comment: Plenary talk, MESON2004 Conference Proceedings, Crakow, June 4-8 200
Important configurations for NN processes in a Goldstone boson exchange model
We study the short-range nucleon-nucleon interaction in a nonrelativistic
chiral constituent quark model by diagonalizing a Hamiltonian containing a
linear confinement and a Goldstone boson exchange interaction between quarks. A
finite six-quark basis obtained from single particle cluster model states was
previously used. Here we show that the configurations which appear naturally
through the use of molecular orbitals, instead of cluster model states, are
more efficient in lowering the six-quark energy.Comment: 17 pages, RevTe
Nucleon-Nucleon interaction in a chiral constituent quark model
We study the nucleon-nucleon (NN) problem as a six-quark system in a
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between the quarks. This interaction has a long range Yukawa-type
part, depending on the mass of the exchanged meson and a short range part,
mainly responsible for the good description of the baryon spectra. We calculate
the NN potential in the adiabatic approximation as a function of Z, the
separation distance between the centres of the two three-quark clusters. The
orbital part of the six-quark states is constructed either from the usual
cluster model states or from molecular orbital single particle states. The
latter are more realistic, having proper axially and reflectionally symmetries.
In both cases the potential presents an important hard core at short distances,
explained through the dominance of the [51]{FS} configuration. However in the
molecular orbital basis the core is less repulsive, as a consequence of the
fact that this basis gives a better upper bound for the energy of the six-quark
system. We calculate the potential for the 3S1 and 3S0 channels with two
different parametrizations. We find a small (few MeV) attractive pocket for one
of these parametrizations. A middle range attraction is simulated by the
addition of a sigma-meson exchange interaction between quarks, of a form
similar to that of the pseudoscalar meson exchange. The present study is an
intermediate, useful step towards dynamical calculations based on the
resonating group method.Comment: 12 pages, 3 eps figures (with aipproc.sty). Talk presented by D.
Bartz at the International Workshop on Hadron Physics "Effective Theories of
Low Energy QCD", Coimbra, Portugal, September 10-15, 199
Probabilities in nonorthogonal basis: Four--quark systems
Four-quark states may exist as colorless meson-meson molecules or compact
systems with two-body colored components. We derive an analytical procedure to
expand an arbitrary four--quark wave function in terms of nonorthogonal color
singlet--singlet vectors. Using this expansion we develop the necessary
formalism to evaluate the probability of physical components with an arbitrary
four-quark wave function. Its application to characterize bound and unbound
four--quark states as meson-meson, molecular or compact systems is discussedComment: Accepted for publication in PR
Effective Action Method for Computing Next to Leading Corrections of Models
We compute the corrections of next to leading order in the
expansion to the effective potential of a system described by a Ginzburg-Landau
model with components and quartic interaction, in the case of spontaneous
symmetry breaking. The method we apply allows to generalize in a simple way the
so-called Self-Consistent Screened Approximation (SCSA).Comment: p. 8, LATEX, DFF 193/9/199
On a three-body confinement force in hadron spectroscopy
Recently it has been argued that a three-body colour confinement interaction
can affect the stability condition of a three-quark system and the spectrum of
a tetraquark described by any constituent quark model. Here we discuss the role
of a three-body colour confinement interaction in a simple quark model and
present some of its implications for the spectra of baryons, tetraquarks and
six-quark systems.Comment: 19 pages (RevTeX), addition of new material regarding the NN
interaction, more accurate discussion of the baryonic case, accepted for
publication in Phys. Rev.
Skyrme density functional description of the double magic Ni nucleus
We calculate the single particle spectrum of the double magic nucleus
Ni in a Hartree-Fock approach using the Skyrme density-dependent
effective interaction containing central, spin-orbit and tensor parts. We show
that the tensor part has an important effect on the spin-orbit splitting of the
proton orbit which may explain the survival of magicity so far from the
stability valley. We confirm the inversion of the and levels at
the neutron number 48 in the Ni isotopic chain expected from previous Monte
Carlo shell model calculations and supported by experimental observation.Comment: 14 pages, 5 figures, typos corrected. arXiv admin note: text overlap
with arXiv:nucl-th/070206
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